1. Field of the Invention
The present invention relates to an image display (a so-called plasma addressed electro-optical display) using plasma whereby to activate an electro-optical material layer so as to display an image.
2. Description of Prior Art
The resolution and contrast of a liquid-crystal type display unit have been improved by, for example, a so-called active matrix addressing method, in which an active device, such as a transistor, is provided for each display pixel and the active devices are operated.
The foregoing method, however, must use a multiplicity of semiconductor devices, such as thin-film transistors, thus causing a problem of unsatisfactory low manufacturing yield to arise when a display having a large area is manufactured. Thus, there arises a problem in that the cost cannot be reduced.
To solve the foregoing problem, a method has been suggested which employs discharge plasma as active devices in place of the semiconductor devices, such as MOS transistors and thin-film transistors.
An image display apparatus (hereinafter called a "plasma addressed electro-optical display") has a stacked structure composed of a liquid crystal layer, which is an electro-optical material layer, and a plasma cell, in which plasma discharge takes place. A thin and dielectric-material plate made of glass and the like is disposed between the liquid crystal layer and the plasma cell.
The plasma addressed electro-optical display has a structure that the plasma cell is divided into linear plasma chambers by barrier ribs. The plasma chambers are sequentially switched and scanned, and signal voltages are synchronously applied to transparent electrodes opposite to the plasma chambers in such a manner that the liquid crystal layer is interposed. Thus, the liquid crystal layer is operated.
The plasma addressed electro-optical display includes discharge electrodes which are formed by a relatively coarse Ni film formed by printing and baking Ni paste.
When Ni is employed to form the discharge electrodes, the sputtering resistance of the discharge electrodes must be raised. Therefore, a process has been employed in which mercury is diffused in the plasma cell.
On the other hand, terminal electrodes for establishing the connection between the discharge electrodes and an external circuit are made of a material prepared by printing and baking gold or silver paste to improve hermeticity.
As shown in FIG. 1, a discharge electrode 101 and a terminal electrode 102 are connected to each other in a plasma cell surrounded by a frit seal 103. In general, the portion, in which the connection has been established, is covered with a cover glass 104.
When the above-mentioned structure is employed, the terminal electrodes 102, however, easily form amalgams because the terminal electrodes 102 is combined with diffused mercury. Thus, there arises a problem in that mercury diffused in the plasma cell is deprived.
The reason for this lies in that mercury is able to easily reach the terminal electrodes through the discharge electrodes 101 in the form of the coarse Ni film and the cover glass 104 having a small thickness.
When the discharge electrodes 101 and the base glass layer 105 are simultaneously formed on a glass substrate 106 by etching by a sand blast method, the terminal electrode 102 is overlaid on the discharge electrode 101. It leads to a fact that mercury is introduced from upper and lower portions, as indicated with an arrow A or an arrow B shown in FIG. 1. In the above-mentioned case, the problem becomes more critical.
If the terminal electrodes 102 are combined with mercury and therefore mercury diffused in the plasma cell is deprived, the discharge electrodes 101 made of Ni can undesirably easily be sputtered when the discharge electrodes 101 perform discharge. In this case, the lifetime is shortened undesirably. If the discharge electrodes 101 are sputtered, sputtered Ni is allowed to adhere to the thin dielectric plate 107. As a result, the transmissivity of light deteriorates excessively, causing a critical problem for the plasma addressed electro-optical display to arise.
To solve the above-mentioned problem, it might be considered feasible to enlarge the thickness of the cover glass 104. If the cover glass 104 has a large thickness, vapor of mercury cannot pass through the cover glass 104.
In the above-mentioned case, barrier ribs (ribs) 108, however, are easily damaged in the boundary with the cover glass 104. It leads to a fact that a problem arises in that a defective image occurs attributable to leakage of discharge.